In recent years, a number of coffee beverages including instant coffees and canned coffees have been marketed. These products contain a coffee flavor for imparting the aroma of roasted coffee beans.
In the Japanese industry of coffee beverages, a coffee flavor falls within the category of food additives which are regulated by the Japanese Food Sanitation Law. They are defined as natural flavors (for example, a distillate or an extract of coffee beans), artificial flavors obtained by chemical synthesis or mixtures or preparations thereof which are added to foods in order to impart or enrich coffee aroma during a manufacturing or processing step [refer to "Shinteiban Shokuhin Tenkabutsu Hyoji no Jitsumu", ed. by Shokuhin Tenkabutsu Hyoji Kondankai (1990)]. It is considered that the intense and deep aroma of fresh milled coffee beans a day or two after being roasted is the most desirable coffee aroma. Thus it has been required to isolate this desirable natural aroma component as such and add the same as a coffee flavor to various coffee products, since the most effective improvement and enrichment of the coffee aroma can be thus achieved.
In order to satisfy this requirement, attempts have been made to collect the volatile aroma component of roasted coffee beans. As examples of these attempts, the following methods may be cited.
(1) Method for collecting an aroma component evolving during the step of roasting green coffee beans:
In the methods disclosed in, for example, U.S. Pat. Nos. 2,087,602 and 2,156,212, a coffee aroma component containing water is generated by roasting green coffee beans under controlling the volume of gas such as air. However, the coffee aroma component thus obtained also contains undesirable aroma ingredients. Thus, these methods require complicated procedures for eliminating these undesirable ingredients. Furthermore, this aroma component can be hardly condensed or collected. Thus it should be immediately absorbed by an appropriate material, which restricts its application range. PA1 This method suffers from a disadvantage that the aroma is liable to be scattered into the atmosphere and thus hardly collected. PA1 In this method, overheating during the production process is unavoidable, which results in the scattering of the aroma into the atmosphere. PA1 In the case of this method, the aroma component is liable to be lost during the process of recovering the employed organic solvent under reduced pressure. Further, the residual solvent should be severely restricted from the viewpoint of food sanitation. PA1 For example, JP-A-52-87248 (corresponding to U.S. Pat. Nos. 4,101,681 and 4,232,598) has disclosed a method comprising distillation under reduced pressure. However, this method requires a special apparatus for condensing and collecting the aroma component and a refrigerant at an extremely low temperature of -196.degree. C. Further, the scattering of the aroma is unavoidable during the step of returning to normal atmospheric pressure. PA1 For example, JP-A-47-19067 (corresponding to U.S. Pat. No. 4,328,255) has disclosed a method wherein coffee beans are extracted with carbon dioxide in the supercritical state under elevated pressure with heating, while JP-A-61-88853 has disclosed another method wherein extraction is effected in the presence of aqueous ethanol by using a fluid in the supercritical state. However each of these methods requires an elaborate apparatus. PA1 It is feared in,this method that some portion of the desirable aroma component might shift into the water. Thus, it is difficult to obtain an aroma component closely similar to the aroma composition of the roasted coffee beans by this method. Further, the treated coffee beans contain a considerably large amount of moisture, which requires a considerably high disposal cost.
Furthermore, there have been reported a method wherein an aroma component containing water which is obtained by roasting is extracted by using a fluid in the supercritical state as will be described hereinafter and another method wherein it is adsorbed by an adsorbent such as active carbon, synthetic zeolite or silica gel. However, these complicated operations inevitably result in an increase in the cost.
Furthermore, JP-A-61-70944 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") has disclosed a method which comprises roasting green coffee beans by indirectly heating under an inert gas stream and condensing and collecting the aroma component thus generated. In this case, however, the aroma of milled coffee beans after being roasted cannot be utilized.
(2) Method for collecting aroma component evolving during the step of milling roasted coffee beans:
(3) Method comprising mechanically pressing roasted and milled coffee beans under heating and obtaining the aroma component in the form of "coffee oil", i.e., a mixture with glycerides contained in a large amount in the beans:
(4) Method comprising extracting roasted and milled coffee beans with an organic solvent to thereby give the aroma component as "coffee oil":
(5) Method for collecting an aroma component by distilling the coffee oil obtained by the above method (3) or (4):
In addition, JP-A-3-217500 has disclosed a similar method wherein ethanol is added to coffee oil and the obtained mixture is distilled under reduced pressure. This method requires a special apparatus for the distillation under reduced pressure.
(6) Method comprising extracting roasted and milled coffee beans with a fluid at a supercritical state by using, e.g., liquefied carbon dioxide or liquid nitrogen:
(7) Method comprising steam-distilling roasted and milled coffee beans and separating water from the obtained distillate or extracting the aroma component alone from the distillate by using an appropriate organic solvent:
For example, JP-B-50-29027 (corresponding to U.S. Pat. No. 3,615,665; the term "JP-B" as used herein means an "examined Japanese patent publication") has disclosed a method which comprises introducing water-containing, roasted coffee beans in a container, passing a saturated vapor at a high temperature and an elevated pressure therethrough, liberating this vapor via a vent line, closing the line after stabilization, and condensing and collecting the vapor. However it is not clear whether the aroma composition of the coffee beans can be taken out as such or not by this method. Also, this method is disadvantageous in requiring a pressure container of a large capacity.
In accordance with Nippon Shokuhin Kogyo Gakkaishi, 39 (11), 1030-1037, (November, 1992), furthermore, N. Imura et al. have proposed a method for collecting the aroma of Arabica coffee beans alone from a steam-distillate of roasted coffee which is to be added in order to improve the desirability of an instant coffee product, since the aroma of the distillate collected from Robusta coffee beans does not suit consumers' preference. However it cannot be concluded that this method is the best one. This is because it suffers from an increase in the cost, since Arabica coffee beans are much more expensive than Robusta coffee beans.
Further, JP-A-59-109133 has disclosed a method which comprises passing steam, and/or an inert gas through roasted and milled coffee beans and collecting the vapor phase containing a volatile coffee flavor component thus liberated by introducing the same into a solution of an amino-carbonyl reaction product and/or caramel of pH 5 or below without condensation. In the case of this method, the amino-carbonyl reaction product and/or caramel serve as a flavor component, which seriously restricts the utilization sphere of the obtained coffee flavor.
Although there have been proposed various attempts to collect the aroma of roasted coffee beans as discussed above, no satisfactory method therefor has been established so far.
With the diversification in food products in recent years, it is further required in the industry of coffee beverages to develop a coffee aroma component which is as good as by milk flavor and excellent in stability during retorting processing as well in stability over prolonged storage.